1. Field of the Invention
The present invention relates to an external additive used for an electrophotographic toner and to the toner used for a developer for developing an electrostatic latent image in electrophotography, electrostatic recording and electrostatic printing and the like, as well as to an electrophotographic image forming apparatus using the toner.
2. Discussion of the Background
Typically, a developer used in electrophotography, electrostatic recording and electrostatic printing and the like is adhered to an image bearer such as photoreceptors on which a latent image is formed in a developing process; transferred on a transfer medium such as transfer sheets in a transferring process; and fixed on the transfer sheet in a fixing process.
As the developer for developing the latent image formed on the surface of the image bearer, a two-component developer including a carrier and a toner and a one-component developer (magnetic or nonmagnetic toner) which does not need a carrier are known.
As a toner included in the developer, a positively charged toner and a negatively charged toner are available in compliance with electrostatic latent images and the processes. As an additive for a toner positively charged, a charge controlling agent such as nigrosin dyes and quaternary ammonium salt; a coating agent to impart a predetermined chargeability to the carrier such as acrylic resins, fluorocarbon resins and silicone resins, etc.; and the like are known. On the other hand, as an additive for a toner negatively charged, a charge controlling agent such as azo dyes including metals; inorganic powders; organic powders; coating agent for the carrier; and the like are known.
In addition, a method in which inorganic powders and the like such as various metal oxides are mixed with toner particles is proposed for the purpose of improving the fluidity and the chargeability of the toner, and such inorganic powders and the like are called external additives. Also, a method in which the surfaces of the inorganic powders are optionally treated with a specific silane coupling agent, a titanate coupling agent, a silicone oil, organic acids, etc. and a method in which the surfaces are optionally coated with specific resins are proposed for the purpose of improving the hydrophobicity and the chargeability of the surface of the inorganic powders. As the inorganic powders, for example, silicon dioxide (silica), titanium dioxide (titania), aluminium oxide, zinc oxide, magnesium oxide, cerium oxide, iron oxide, copper oxide, tin oxide, etc. are known.
Particularly, the silica and hydrophobized fine particles of silica whose silanol group is substituted with an organic group by reacting fine particles of titanium oxide with organic silicon compounds such as dimethyldichlorosilane, hexamethyldisilazane and silicone oil are used.
Among these additives, silicone oil is preferably used as the hydrophobizer because it has sufficient hydrophobicity and when included in the toner, the toner has excellent transferability due to the low surface energy of the silicone oil. The hydrophobicity of the silica treated with the silicone oil is disclosed in Japanese Patent Publication No. 7-3600 and Japanese Patent No. 2568244. In addition, Japanese Laid-Open Patent Publications Nos. 7-271087 and 8-29598 disclose the content of the silicone oil and the content ratio of a carbon atom in an additive.
In order to obtain the charging stability of a developer under a condition of high humidity when hydrophobizing inorganic fine particles which are mother agents of an additive, the above-mentioned content of the silicone oil and the hydrophobicity are sufficient.
However, it is not positively attempted to decrease the adherence of the developer to a member contacting the developer such as a contact charger, a developer carrier (a sleeve), a doctor blade, a carrier, an electrostatic latent image bearer (a photoreceptor) and an intermediate transfer medium by taking advantage of the low surface energy which is one of important properties of the silicone oil. Particularly, background fouling and hollow characters (portions on which the developer is not transferred) of characters, lines, and the edge and the center of dot images after image transfer due to the strong adherence of the developer to the photoreceptor cannot be improved only by adjusting the content and the hydrophobicity of the silicone oil. Further, hollow characters due to the inability of the developer to transfer on a concave portion of a transferring member having many concavities and convexities cannot be improved either.
Japanese Laid-Open Patent Publication No. 11-212299 discloses inorganic fine particles including a specific content of the silicone oil as a liquid content. However, such a definition of the quantity cannot satisfy the above-mentioned properties. In addition, it is neither referred to how the silicone oil or a component capable of performing an equivalent function to the silicone oil is treated and adhered to inorganic particles nor referred to the effective structures of the silicone oil and the component. Further, information of mixed condition of the silicone oil and the component with the inorganic fine particles is not available.
Accordingly, an object of the present invention is to provide an external additive for use in a developer producing a high-quality image having appropriate image density and very little background fouling even when producing many copy images for a long period of time without contaminating a charger; an image developer; a photoreceptor; and an intermediate transfer medium, and to provide an electrophotographic image forming apparatus using the developer.
In addition, another object of the present invention is to provide an external additive for use in a developer producing a stable image having high image-reproducibility on any transfer medium without producing a blurred image; an image with hollow characters; and scattering toner, and to provide an electrophotographic image forming apparatus using the developer.
Briefly these objects and other objects of the present invention as hereinafter will become more readily apparent can be attained by using hydrophobized inorganic fine-particles having not more than a specific particle diameter, and including at least a compound having an organosiloxane structure in the solvent-treated residual components or a ring siloxane structure in the pyrolysates of the solvent-treated residual components as an external additive for an electrophotographic toner.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.